Gastroparesis (although it is translated into various terms such as gastric incomplete paralysis or gastric contents lingering, the word “gastroparesis” itself is used in this specification) presents symptoms including nausea, vomiting and abdominal bloating, and is a chronic gastric functional disorder which leads to leading to delayed gastric emptying (Hornbuckle K, Barnett J L (2000) J Clin Gastroenterol, 30, 117-124). Gastroparesis may be caused by the cutting of the vagus nerve or by diabetes, but it may also occur without any identifiable cause (idiopathic gastroparesis). Although various conditions are associated in gastroparesis in a complex manner, it is said that abnormalities in gastric myoelectrical activity (GMA), such as increase in dysrhythmia and decrease in the frequency of spike burst, are deeply involved therein (Chen J, McCallum RW (1992) Am J Gastroenterol, 87,477-482). Recently, gastric electrical stimulation has been attracting attention as means for treating drug-resistant, obstinate gastroparesis, and several patent applications have been filed mainly in the United States (see patent documents 1 and 2).
However, in those apparatuses pertaining to gastric electrical stimulation used so far, a circuit to generate stimulation waveforms and a battery (power source) are implanted in the body in the same manner as many implanted-type pacemakers. Therefore, re-operation is necessary for battery replacement. Since major target patients for gastric electrical stimulation are aged persons, such an apparatus requiring a surgical operation periodically imposes a heavy burden on them.
Further, there are two types of stimulations in gastric electrical stimulation: long pulse stimulation (LPS) and short pulse stimulation (SPS). The former is a stimulation with a frequency close to the intrinsic gastric slow wave frequency (IGF) and with a pulse width of 300 ms or more (Bellahsene B E, Lind C D, Schirmer B D, et al. (1992) Am J Physiol, 262,G826-834; Forster J, Sarosiek I, Delcore R, et al. (2001) Am J Surg, 182,676-681; GEMS Study Group. (1996) Gastroenterology, 110,A668; Eagon J C, Kelly K A (1995) Neurogastroenterol Motil, 7,39-45). The latter is a stimulation with a frequency about 4-fold of the intrinsic gastric slow wave frequency and with a pulse width of 1 ms or less (Familoni B O, Abell T L, Nemoto D, et al. (1997) Dig Dis Sci, 42,892-897). Both stimulations have been confirmed to have certain improvement effect on gastroparesis, but actually, apparatuses to provide long pulse stimulation are employed little. This is because long pulse stimulation consumes about 1000 times as much electricity as short pulse stimulation and thus sufficient electricity cannot be secured with the above-mentioned battery-implanted type apparatus.
The above-described problems of the re-operation because of battery expiration and the shortage of electricity in generating long pulse stimulation can be solved by implanting in the body only the circuit to generate stimulation waveforms, locating a power source outside of the body, and supplying electricity through a lead. However, this means that the lead is penetrating the skin, and there is a danger of bacterial infection or the like from the penetration site.
[Patent Document 1] the specification of Japanese Patent No. 2710864
[Patent Document 2] the specification of U.S. Pat. No. 6,115,635
As described so far, the conventional, gastric electrical stimulation apparatus imposed a heavy burden on patients and was virtually impossible to provide long pulse stimulation.
The present invention has been made under such circumstances. It is an object of the present invention to provide a gastric electrical stimulation apparatus which imposes a less burden on patients and is also capable of providing long pulse stimulation.